The National Tritium Labeling Facility (NTLF) was funded on 08/01/82. During its first year the facility was built and equipped; it became fully operative in August 1983. It is now engaged in an active program of aiding biomedical researchers to obtain needed and commercially-unavailable tritium labeled compounds. For the ten month period Oct. 1983-Aug. 1984 this has averaged two labeling operations per month and has aided scientists from as far away as New York and Hawaii. The compounds labeled have included prednisone, nicotine, pheromones, gibberelic acids, endorphins, tabtoxinine- -lactam, and tuftsin. The tritium facility is now fully staffed, and because knowledge of its labeling services is growing, requests for tritiation help are also growing; the facility is expected to reach its full capacity (one tritiation per week) in its 3rd year. The core research is being rapidly pursued. During the 2nd grant year one manuscript was accepted for publication in the Journal of Physical Chemistry, and a second manuscript was submitted to that journal in September 1984. The core research summarized in these manuscripts contributes to our understanding of the processes involved in "excitation labeling" (exposure of organic compounds to a stream of T2 that has been passed through a microwave generator). The knowledge gained in this work has increased the efficiency with which the excitation procedure can be used. This research will be enhanced in the 3rd and succeeding grant years by the tritium-NMR capability that has been added. The position(s) of tritium in all labeled compounds can now be determined, and this greatly aids the mechanistic interpretations regarding the tritiation procedures that have been used. The staff of the NTLF is doing collaborative research (co-authorship of published papers) with Professor Richard E. Moore of the University of Hawaii; the work is directed towards identifying the cell-membrane receptor sites for the potent tumor promoters lyngbyatoxin and aplysiatoxin. The staff is also collaborating with Professor A.J. Kresge of the University of Toronto on hydrogen-isotope effects on NMR spectra. This kind of collaborative research will be expanded with the increasing use of the NTLF by biomedical researchers.